Culms 2-40 cm × 0.5-1.5(-2) mm. Leaves: apex of distal leaf sheath obtuse to acute, tooth to 0.3 mm. Spikelets lanceoloid to subcylindric or ovoid, 5-10(-20) × 2-3(-4) mm, apex acute (to rounded); proximal scale empty, encircling ca. 2/3 of culm; floral scales 25-100(-200), 8-12 per mm of rachilla, orange brown to stramineous, 2(-2.5) × 1-1.3 mm, midribs mostly keeled, ovate, apex narrowly rounded to subacute. Flowers: perianth bristles present or often absent, 5-8, brown, stout, rudimentary to slightly exceeding tubercle; stamens (2-)3; anthers brown to yellow, 0.3-0.7(-1) mm; styles 2-3-fid. Achenes 0.9-1.1(-1.5) × 0.7-1.1 mm. Tubercles depressed, subdeltoid, 0.1-0.3(-0.4) × 0.6-0.9(-1) mm, 1/10-2/5 as high as wide, 1/4 or less as high as achene, 9/10 as wide as achene, very rarely 2/5 as high as achene (in E. engelmannii var. robusta). 2n = 10. Fruiting spring-fall. Fresh shores, marshes, disturbed places; 30-2400 m; Alta., B.C., Man., Ont.; Ala., Ariz.., Ark., Calif., Colo., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Kans., Ky., Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., N.H., N.J., N.Mex., N.Y., N.Dak., Ohio, Okla., Oreg., Pa., R.I., Tenn., Tex., Va., Wash., W.Va., Wis. Robust plants known only from Missouri and described as Eleocharis engelmannii var. robusta have well-developed caudices, culms to 2 mm wide (pressed), spikelets to 2 cm, floral scales to 2.5 mm and slightly cartilaginous, styles mostly trifid, achenes to 1.5 × 1 mm, and tubercles 0.3-0.5 × 0.7-1 mm and to 2/5 as high as achene. Some specimens are intermediate between E. engelmannii and E. obtusa, or rarely with E. lanceolata. I have not seen specimens to verify literature reports of E. engelmannii from Manitoba, Connecticut, Delaware, Idaho, New Hampshire, North Carolina, Oregon, Rhode Island, South Carolina, South Dakota, or Vermont.